In "Omens, Part 1": Tygra, who spends the entire episode picking on and making fun of Lion-O, stepping in and saying he's got his brother's back when Lion-O is shouted down by the cats who were tormenting the captured lizards.
In "Omens, Part 2":
After Lion-O uses some tech he'd found earlier to save them. Claudus walks up to him, and gives him a silent salute of respect. Obviously this is his way of apologizing for his lack of respect and understanding earlier. It's a surpisingly touching gesture, coming from him.
And of course later when Claudus tells Lion-O he's proud of him, just before he dies.
Let's not forget Claudus doing the famous "Thundercats, HO!" before he charges off to face Grune. Anyone who watched the old show surely felt their inner child squealing with joy at hearing those words from the man who once was Lion-O, so long ago...
"Song of the Petalars,": Many parts, doubling as a Tear Jerker.
In "The Tower of Omens".
A little blink-and-you'll-miss-it moment, when Panthro congratulated the group.
Panthro: I can't believe I finally found it! Guess all it took was the right partners.
Everyone going out of their way to help Lion-O get the Book of Omens at the end. Bonus points go to Wilykit and Kat for trying to defend a fallen Panthro from freakin Mumm-Ra! First Panthro blocks Mumm-Ra, then the twins try there hand, and then Tygra pops up out of nowhere and keeps him busy!
A subtle one, but during a gag where Panthro is the victim (it's before the Defrosting Ice King phase begins), Lion-O and Tygra exchange an amused smile. It's pretty sweet to see them share such a simple moment like that.
Yes, acting as a total badass while still hugging the bear in front of teasing kitss. He's not ashamed, aahh!
Wilykit riding on top Aburn during the musical sequence in "Sight Beyond Sight". It was a very sweet moment.
After questioning Lion-O's suitability for the Sword of Omens in "The Forest of Magi-Oar", Tygra expresses his support for and belief in his brother by telling him he simply needs to believe in himself to use it properly.
In "Into the Astral Plane"
The flashbacks between Tygra and Cheetara, but given how Lion-O-centric the series has been up until now, it's refreshing to see other members of the main cast being fleshed out not only as individuals but in terms of their relationship to the rest of the Thundercats as well.
Cheetara kissing Lion-O. So far she hasn't shown awareness of the brothers' feelings. Then she kisses him on the cheek revealing he's more than the king to her. He's someone different and special.
In "Between Brothers",
The Relationship Upgrade that takes place between Tygra and Cheetara. More specifically, the flower he left for her turned out to have magical properties, allowing her to maintain her constant vigil by eating its petals. And she's kept the heart of the flower all this time.
Little Tygra didn't betray Lion-O: he ran to their father for help, and even admitted he was at fault.
Tygra and Cheetara's smile when Lion-O says that he's happy about there Relationship Upgrade. It's nice to see that Tygra really wouldn't want to hurt Lion-O's feelings. Especially after all the posturing he'd been doing lately.
Kit out right refusing to believe that Lion-O is dead is this or a Tear Jerker.
The kittens hugging Lion-O in "Trials of Lion-O part 2"
The flashback with Baby Tygra, and his late mother.
Lion-O acting all brotherly towards Tygra throughout the episode, showing just how much their relationship has changed since the start of the series.
Tygra: Tell me, Lion-O, is it my destiny to always lose the things I care most about?
Lion-O: You aren't gonna lose me, brother.
In "The Pit" Lion-O refuses to fight against Pumyra despite her blaming him for the suffering she went through and her desire to kill him, but he also refuses to lay down and die: "I said I would stand with you, and I intend to." In spite of everything he has total faith in her, and he's willing to bet his life on it.
After the fight and Lion-O's words to Pumyra, the crowd who's more than used to seeing and even enjoying these deadly battles immediately claim for both Lion-O's and Pumyra's freedom.
Dobo, despite still considering Panthro a friend, is still resentful of Panthro for seemingly abandoning him and clearly has issues with cats, finding them untrustworthy, so it's quite something to see how he mellows out during the episode. From giving Lion-O the opportunity to go free if he beats Pumyra rather than having to fight 100 battles, to being touched by Panthro admitting that the reason he escaped without Dobo was because he learned that he and Dobo would be forced to fight to the death, to his listening to the crowd claiming for both Lion-O's and Pumyra's freedom, which he immediately concedes, having learned that cats can truly be as loyal as dogs.
In the "Curse of Ratilla" the first enslaved Cat Lion-O talks to is an old man who, though in a bad state, is elated to see his king and says that he never lost faith in him, even when others said Lion-O had abandoned them all.
There's also when he's helping Pumyra out of the rubble at the end, he throws her arm around his shoulders and she admits that maybe they could use a little mercy in their quest.
It all culminates in the end of "Birth of the Blades," when Pumyra caresses his face and calls him by name for the first time, after he chose to save her life instead of getting the Sword of Plundarr. Lion-O doesn't mind at all. The whole dialogue:
Lion-O spends much of "Recipe for Disaster" trying to catch Pumyra's attention so he can talk to her about some of he feelings he's had for her recently and all his attempts fail miserably. Finally he's advised to just "Be Yourself" but before he has a chance to try Mumm-Ra attacks and corners Pumyra, prompting Lion-O to save her (again). She rewards him with an enthusiastic kiss on the cheek.
The same episode has Pumyra tenderly helping a baby flying frog that had fallen out of its nest.
Despite "What Lies Above Part 2" being a heck of a Wham Episode and quite a bittersweet one, there are a couple of nice moments to help ease the pain. Tygra comes to save Lion-O from getting killed by Pumyra, assuring him that he'll never be alone, reinforced by how many responded to Gondor Calls for Aid. And despite losing the Tech Stone and having his heart broken, Kit reminds Lion-O that he's helped unite many races of Third Earth, and there's still hope.